Prior research on marriage has tended to focus on cross-sectional differences between the married and unmarried, with little attention to selectivity, change over time, or the substantive implications of statistically different means. This paper addresses these issues and provides a perspective for thinking about the relative benefits of marriage. It examines how transitions into marriage and cohabitation are associated with change over time in multiple measures of well-being and social relationships. Change score methods are used to control for differences in unmeasured variables that may affect the link between union status and various individual and couple-level outcomes. The analysis shifts emphasis to trajectories as opposed to snapshots, and it draws attention to the variability in outcomes within and across union statuses. Results show no difference between the effects of moving into marriage compared to cohabitation on happiness, depression, contact with parents, or time spent with friends; they show some difference in health, self esteem, intergenerational relationships, and couple relationships. Nonetheless, when mean differences are statistically significant, they tend to be small and appear to dissipate over time. The authors conclude that similarities between marriage and cohabitation are more striking than differences.